Electric pickup



Aug. 27, 1946.v l H1 Us Y `2,406,597

ELECTRIC PICKUP Eiled Sept. 7, 1944" Harold T. Paus, bg Vm/176 Ami/M1 H is Attorneg.

Patented Aug. 27, 1946 ELECTRIC PICKUP Harold T. Faus, Lynn, Mass., assgnor to General Electric Company, a corporation of -New kYork Application September 7, 1944, Serial No. 553,019

6 Claims. (Cl. 17a-100.41)

My invention relates to Vibration translating devices, such as phonograph pickups, and particularly to such devices of the electromagnetic type having movable coils.

Yltis an object of my invention to provide an improved electric pickup of simple and rugged construction andhaving a moving system oi very loW- inertia. j yItis another object of my invention to provide `an improved phonograph pickup having a vvibratable stylus arm and associated coil oi very light weight and low inertia which will track inthe sound groove of a record with very slight pressure on the stylus.-

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig'. 1 represents a portion of a phonograph provided with a pickup embodying my invention; Fig. 2 is an enlarged view, partly in section, of the pickup head shown in Fig. 1; Fig. 3 is a View, ,partly broken away, 01,1 the line 3-3 of Fig. 2; 4 is a bottom plan View of the portion of the pickup shownA in Fig. 3; and Fig. 5 is an enlarged sectional View of the stylus arm and coil assembly of the pickup.

Referring now .to the drawing, the phonograph in Fig, 1 comprises a turntable `l and a tone arm 2 both of which are mounted on a suit,- able supporting structure a portion of which is indicated at 3, the turntable being driven in the usual manner by a motor mounted Awithin the supporting structure. The tone arm 2 is pivotally mounted on a bracket 4 rotatably mounted in the support 3, and a pickup 5 is mounted onthe arm 2 in a position such that a stylus 6 mounted on the pickup may engage the sound track of a record 'l on the turntable. The weight of the tone arm and pickup to the right of the bracket 4 is balanced by a suitable counterweight B to the left of the bracket 4 so that a very small unbalanced weight remains for holding the stylus 6 on the record. Electric voltage variations produced by the pickup 5 in accordance with vibrations of the stylus 6 are amplified by suitable ap- -paratus (not shown) which is connected to the pickup through Wire leads 9 the ends of which have been indicated as entering the interior of the structure 3 through the base of the bracket LV The details of construction of the pickup 5 are clearly shown in Figs. 2 to 5, inclusive. The supporting head of the pickup includes a block Il] ofV rigid insulating material secured in the end of the tone arm 2 by a setscrew Il. A magnet structure l2 and a weight i3 are rigidly secured to *l theblock I0 by a screw' ld. The stylus 6 is mounted onthe core structure l2 and a ycoil l5 is secured on a nonmagnetic support i6 of aluminum'or other suitable light material which is connected rigidly to thel stylus 6 for Vibration therewith. The coil l5 is provided with terminals il, which are connected to the leads 9 through suitable conductors i8 secured to .the block l0 byvscrews I3, only one of the conductors i8 and screws I9 being shown on the drawing. A shield 25 enclosing the sides and bottom of the pickup and held on the tone arm 2 by a collar 2| is provided to enclose the pickup, and a cover 22 is secured over the front and top of the pickup and held in place by a screw 23. The cover 2i! is provided with an opening 24 at its forward end and the stylus 6 extends beyondvthe pickup through the opening 24 into position for engagement with the sound track of a record.

As shown in Figs. 3 ande, the magnet structure i2 comprises two bar magnets 25 and 26 yoked together at their top ends by a bar 2l of magnetic material. A block 2S of brass or other suitable nonmagnetic material is soldered or otherwise rigidly secured within the magnetic structure in engagement with the magnets 25 and 25 and the yoke 27. The lower ends of the magnets 25 and 26 are provided with pole pieces 29 and 30, respectively, which are spaced apart at the lower end of the structure and have faces of .circular cross section, as indicated in Fig. 4. The block 23 is somewhat shorter than the bar magnets and a core 3l of magnetic material is secured in the block 28 in a recess 32 as indicated in Fig. 5. The stylus 3 and coil l5 are resiliently mounted on the core 3|, the coil l5 being concentric with the faces of the pole pieces 29 and 30.. The details of construction of the stylus arm and coil assembly are clearly shown in Fig. 5. The stylus 5 is mounted in a sleeve 33 whichvhas a pin 34r projecting upwardly from the other end thereof. The sleeve 33 is provided with an annular shoulder 35-and the coil support IS is securely mounted on the sleeve 33 in engagement with the shoulder 35. The stylus arm thus comprises the pin 34 and the sleeve 33 with the stylus 6 supported in the lower end of the sleeve. The

stylus is preferably a sapphire or other suitable jewel. The magnetic core 3l is of circular cross section and has an enlarged portion 36 mounted in alignment with the pole pieces 29 and 30 and equally spaced from the pole pieces. The core 3| is provided with a downwardly opening central recess 31, and a block 38 of rubber or other suitable resilient material is positioned in the recess, and the pin 34 is pressed into a central opening 39 in the block 38. The coil supporting member I6 comprises a conical lower portion and a cylindrical upper portion arranged between the pole pieces 29 and 30, the coil l5 being mounted on this upper portion'concentrically with the pin 34 and the core 3|. The magnets 25 and 26 are arranged to produce flux in the same direction between the pole pieces and when the stylus 6 is displaced laterally, as viewed in Fig. 5, the coil l5 rotates about an axis at right angles to the flux path between the pole pieces and passing through the upper portion of the pin 34. This motion generates a voltage in the coil which is proportional at any instant to the velocity of the movement of the stylus. Any displacement of the stylus at right angles to the lateral displacement will produce no voltage in the coil since both sides of the coil will be moved in the same direction through the eld between the pole pieces.

The structure of the pickup is suiciently rigid to prevent any resonant vibrations at audible frequencies and since the moving mass associatedv with the coil l5 is extremely small the stylus 6 can follow accurately the variations of the sound track of a record.

During the operation of the phonograph a record 1 is placed on the turntable I which is rotated while the pickup 5 is placed in position with the stylus 6 in engagement with the sound groove of the record. The stylus is vibrated laterally in accordance with the sound track and the coil l5 oscillates about its above mentioned axis through the upper portion of the pin 34 and produces voltage variations corresponding to the vibrations of the stylus. These voltage variations are amplified in the usual manner by suitable apparatus connected to the leads 9.

From the foregoing it is readily apparent that I have provided a phonograph pickup of simple and rugged construction which may be made with a very small moving mass so that the stylus may acurately follow a record sound track over a wide range of audible frequencies.

While I have illustrated my invention in connection with a particular form of phonograph pickup, other applications will readily be apparent to those skilled in the art. I do not, therefore, desire my invention to be limited t0 the particular arrangement illustrated and described, and I intend by the appended claims to cover all modifications which fall within the spirit and scope of my invention. y

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric pickup or the like comprising a head between said pole pieces and spaced there-.

from, said core having a recess therein opening outwardly between said pole pieces, a stylus arm having a stylus at one end thereof and being resiliently supported at its other end in the recess in said core, said stylus arm extending outwardly from said head for holding said stylus in a position for engagement with a record sound track,

' and means including a coil spaced from and sursupporting head, a permanent magnet structure mounted on said head and providing two spaced pole pieces, a magnetic core supported on said head between said pole pieces and spaced therefrom, a stylus arm having a stylus at one end thereof, means including a block of resilient material for supporting the other end of said stylus arm on said core with said arm extending outwardly for holding said stylus in a position for engagement with a record sound track, said block of resilient material constituting the sole connection between said stylus and said core,

rounding said core between said pole pieces and supported solely by said stylus arm for translating into electrical variations the vibrations of said stylus.

3. An electric pickup or the like comprising a supporting head, a permanent magnet structure mounted on said head and providing two spaced pole pieces, a magnetic core supported on said head between said pole pieces and equally spaced therefrom, said core having a central recess therein opening outwardly between said pole pieces, a stylus arm having a stylus at one end thereof, a block of resilient material arranged in said recess for supporting said stylus arm and for holding said stylus in a position for engagement with a record sound track, and means including a coil spaced from and surrounding said core between said pole pieces and supported solely by said stylus arm for translating into electrical variations the vibrations of said stylus.

4. An electric pickup or the like comprising a supporting head, a permanent magnet structure mounted on said head and providing two spaced pole pieces, a magnetic core supported on said head between said pole pieces and equally spaced therefrom, said core having a recess therein opening outwardly between said pole pieces, and a stylus arm having a stylus at one end thereof and being resiliently supported at its other end in the recess in said core, said stylus arm extending Youtwardly from said head for holding said stylus in position for engagement with a record sound track, a hollow member secured to said stylus arm outwardly of said core and having a portion between said core and said pole pieces and concentric with respect to said core, and means including a coil on said concentric portion of said member for translating into electrical variations the vibrations of said stylus.

5. An electric pickup or the like comprising a supporting head, a U-shaped permanent magnet structure mounted on said head and providing two spaced pole pieces, a body of nonmagnetic material supported within said structure, a magnetic core supported on said body of materialand having a portion extending between said. pole pieces and equally spaced therefrom, said lcore having a recess Vtherein opening' outwardly between said pole pieces, a stylus rarm having a stylus at one end thereof and being resiliently supported at its other end in therecess in said core, said stylus arm extending outwardly from said head for holding said stylus in a position for engagement with aV record sound track, and means including a coil surrounding said core between said pole pieces and supported solely by said 5 stylus arm for translating into electrical variations the vibrations of said stylus.

6. An electric pickup or the like comprising a supporting head, a magnetic structure comprising two bar magnets having a. connecting yokel at one end and separate spaced pole pieces at the other end, a body of nonmagnetic material rigidly supported between said bar magnets, a core of magnetic material (supported on said body of material and having a portion arranged between said pole pieces and equally spaced therefrom, said core having a central recess therein between said pole pieces and opening outwardly, a stylus arm having a stylus at one end thereof and having its other end resiliently supported in therecess in said core, said stylus arm extending outwardly from said head for holding saidy stylus in a position for engagement with a record sound track, and means including a coil surrounding said core between said pole pieces and supported solely by said stylus arm for translating into electrical variations the vibrations of saidstylus.

HAROLD FAUS. 

